Embodiments of the invention relate generally to superconducting magnet systems, and in particular, to a quench protection apparatus which protects superconducting coil assemblage from damage during a quench.
Superconducting magnet systems having relatively large energies are currently used in many applications. For example, superconducting magnet systems, storing energy of up to tens of mega Joules, are constructed for Magnetic Resonance Imaging (MRI) systems which are now being routinely used in large numbers in clinical environments for medical imaging. A part of such a MRI system is a superconducting magnet system for generating a uniform magnetic field.
Superconducting magnets tend to be inherently unstable in that the temperature of a coil region of the magnet can rise relatively rapidly, due to a disturbance within the magnet itself or due to a cause external to the magnet. Such a temperature rise causes a quenching of that coil region, i.e., the superconducting coil goes from its superconducting state of essentially zero resistance to a resistive state. When such coil region gets hot very rapidly the stored energy within the magnet tends to become dissipated rapidly into that finite resistive region and may severely damage the magnet, even in some cases causing an actual melting of the superconducting wires in the coil region.
Accordingly, it is necessary to provide a quench protection apparatus for protecting the superconducting coil assemblage. In general, the quench protection apparatus is designed such that the “quench” is propagated as quickly as possible after initiation, that is, if some area of a coil region quenches, the superconducting magnet system is designed so that the entire superconducting coils become resistive as soon as possible. This design criteria results in lower voltages and lower peak temperatures in superconducting magnet compared to un-protected magnet quench since the stored energy of the superconducting magnet system is dispersed throughout a larger mass.
Known quench protection techniques include using a quench-detection signal (from the electrical center of the superconducting coil assemblage of the superconducting magnet system) directly supplying an energy dump resistor or directly powering wide-area heaters located on the superconducting coil assemblage.
For these and other reasons, there is a need for providing a new quench protection apparatus to protect the superconducting coil assemblage from damage during a quench.